If there's many more numbers than intervals, iterating over the number is indeed a bad idea. But if I understand your demand correctly, the desired can be achieved by iterating over intervals (or rather, over their min and max values: 2..5 and 4..7 is the same as 2..7 and 4..5 regarding coverage).

So you would have to create two arrays (e.g. @min and @max) holding respectively the lower and higher bounds of all intervals. Then: